Subsurface flow constructed wetlands treating municipal wastewater for nitrogen transformation and removal

Abstract

Research was conducted on pilot‐scale, subsurface flow constructed wetland systems treating municipal wastewater. Increasing the hydraulic retention time (HRT) from 1.7 days to 4.3 days reduced the mean effluent NH 4 concentration by 2.7 mg N/L. Hydroperiod manipulation caused a 2.9‐mg N/L decrease in effluent NH 4 . The influent NH 4 concentration for the 9‐month study period averaged 21 mg N/L. The lowest average effluent NH 4 concentration observed in single‐stage treatment cells was 13 mg N/L. The mean effluent NH 4 concentration from the second‐stage cells of two wetland cells in series was 10 mg N/L. During the period from May through September, the second‐stage cells produced an effluent NH 4 concentration of 6 mg N/L. A variable‐order kinetic model for sizing the second‐stage cells of a series system yielded a coefficient of determination, r 2 of 0.94 for the summer NH 4 removal data. The predicted HRT to reduce NH 4 from 20 mg N/L to 5 mg N/L was 3.9 days, if the cells were subjected to cyclic draw and fill.